Most people are not well trained, and they are unobservant. I learned to ride a dirt bike when I was ten, and I’m still riding motorcycles. Riding in the dirt taught me to read the trail conditions and to react to them quickly. A large rock or some unexpected soft sand could cause a spill. In other words, I learned early on how to pay attention.
Most people don’t learn to drive until they’re in their mid-to-late teens. Their training period is short, and they generally learn just enough to pass the driver’s exam. (I’ve been told it’s much easier and cheaper to get a license here in the U.S. than in other places, so what they learn might not be much.)
I’ve referred in several threads to the Left Seat Passenger or Left Seat Zombie. LSPs are not really in control of their cars, but are merely along for the ride; they just happen to have a steering wheel in front of them. They talk on their mobile phones, talking to their passengers, listening to the radio, and so forth. These are not, in themselves, bad things; but they become bad things when they interfere with the operation of the vehicle. Inattention can lead to collisions.
Headlight switches have three positions: OFF, PPARKING/INSTRUMENT, and ON. Very often people will, thorugh inattention, not put the switch in the ON position. There are lots of lights in the city. Parking lots and streets can be so brightly lit that people don’t notice that their headlights are off. They see that their instrument panel is lit, and so they have no reason to think that their headlights are not on.
When you flash your lights at them, they are apt to think “Why is that person flashing his lights at me? What a Jerk!” It seems to me that many people have lost the comprehension of, or never learned, common signals. When I learned to drive, turning one’s lights off briefly was a signal to check one’s headlights. Flashing the high beam was a signal to the other driver to please dim his lights, or to verify that they are actually in the low-beam mode. Nowadays (in my observation) the dark-light driver will as often as not, not turn on his headlights. The high-beam driver will more often than not, not respond.
So to recapitulate: Drivers inadvertantly do not turn on their headlights. They don’t notice because they are often in brightly lit areas and their instrument lights indicate to them that their headlights are on. They don’t respond to signals because they have no inkling that their lights are off, and they don’t understand what turning one’s lights off and on again means.